Association Between Decreased Srpk3 Expression and Increased Substantia Nigra Alpha-Synuclein Level in an MPTP-Induced Parkinson's Disease Mouse Model

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is caused by the loss of dopaminergic neurons in the substantia nigra (SN). However, the reason for the death of dopaminergic neurons remains unclear. An increase in alpha-synuclein (alpha-syn) expression is an important factor in the pathogenesis of PD. In the current study, we investigated the association between serine/arginine-rich protein-specific kinase 3 (Srpk3) and PD in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model and in SH-SY5Y cells treated with 1-methyl-4-phenylpyridinium (MPP+). Srpk3 expression was significantly downregulated, while tyrosine hydroxylase (TH) expression decreased and alpha-syn expression increased after 4 weeks of MPTP treatment. Dopaminergic cell reduction and alpha-syn expression increase were demonstrated by Srpk3 expression inhibition by siRNA in SH-SY5Y cells. Moreover, a decrease in Srpk3 expression upon siRNA treatment promoted dopaminergic cell reduction and alpha-syn expression increase in SH-SY5Y cells treated with MPP+ . These results suggested that Srpk3 expression decrease due to Srpk3 siRNA caused both TH level decrease and alpha-syn expression increase. This raises new possibilities for studying how Srpk3 controls dopaminergic cells and alpha-syn expression, which may be related to PD pathogenesis. Our results provide an avenue for understanding the role of Srpk3 in dopaminergic cell loss and alpha-syn upregulation in SN. Furthermore, this study supports a therapeutic possibility for PD in that the maintenance of Srpk3 expression inhibits dopaminergic cell reduction.